Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S.: Data and R code

Atmospheric deposition of nitrogen (N) influences forest demographics and carbon (C) uptake through multiple mechanisms that vary among tree species. Prior studies have estimated the effects of atmospheric N deposition on temperate forests by leveraging forest inventory measurements across regional gradients in deposition. However, in the United States (U.S.), these previous studies were limited in the number of species and the spatial scale of analysis, and did not include sulfur (S) deposition as a potential covariate. Here, we present a comprehensive analysis of how tree growth and survival for 71 species vary with N and S deposition across the conterminous U.S. Our analysis of 1,423,455 trees from forest plots inventoried between 2000 and 2016 reveals that the growth and/or survival of the vast majority of species in the analysis (n=66, or 93%) were significantly affected by atmospheric deposition. Species co-occurred across the conterminous U.S. that had decreasing and increasing relationships between growth (or survival) and N deposition, with just over half of species responding negatively in either growth or survival to increased N deposition somewhere in their range (42 out of 71). Averaged across species and conterminous U.S., however, we found that an increase in deposition above current rates of N deposition would coincide with a small net increase in tree growth (1.7% per Δ kg N ha-1 yr-1), and a small net decrease in tree survival (-0.22% per Δ kg N ha-1 yr-1), with substantial regional and among-species variation. Adding S as a predictor improved the overall model performance for 70% of the species in the analysis. Our findings have potential to help inform ecosystem management and air pollution policy across the conterminous U.S., and suggest that N and S deposition have likely altered forest demographics in the U.S.

氮气（N）的气溶胶沉积对森林人口统计学和碳（C）吸收的影响是通过多种机制实现的，这些机制因树种而异。先前的研究通过利用区域沉积梯度上的森林资源测量数据，估计了大气氮沉积对温带森林的影响。然而，在美国（U.S.），这些先前的研究在物种数量和分析空间尺度上存在局限性，并且没有将硫（S）沉积作为潜在的协变量考虑。在本研究中，我们对71个树种在北美大陆范围内的氮和硫沉积对树木生长和存活的影响进行了全面分析。我们对2000年至2016年间清查的1,423,455棵树木进行分析，发现分析中绝大多数物种（n=66，或93%）的生长和/或存活受到大气沉积的显著影响。在北美大陆范围内，具有生长（或存活）与氮沉积之间降低和增加关系的物种共存，其中超过一半的物种在其分布范围内对氮沉积的增加表现出负面的生长或存活反应（71个物种中的42个）。然而，从物种和北美大陆范围内平均来看，我们发现沉积量的增加超过当前氮沉积率将伴随着树木生长（每增加Δ kg N ha-1 yr-1增长1.7%）的微小净增长和树木存活（每增加Δ kg N ha-1 yr-1减少0.22%）的微小净下降，同时存在显著的区域和物种间差异。将硫作为预测变量，提高了分析中70%物种的整体模型性能。我们的发现有助于为北美大陆范围内的生态系统管理和空气污染政策提供信息，并表明氮和硫沉积很可能已改变美国的森林人口统计学。